mlab 1415- hematology keri brophy-martinez chapter 6: hemoglobin
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MLAB 1415- Hematology
Keri Brophy-Martinez
Chapter 6: Hemoglobin
Hemoglobin
What is it? Iron- bearing protein which is the main component of the RBC Gives the red cell its color
Synthesis Majority synthesized at the polychromatophilic normoblast stage
Regulation Stimulated by tissue hypoxia Hypoxia causes the kidneys to increase production of EPO, which
increases RBC and hemoglobin production Function
Carry oxygen from the lungs to the tissues Remove CO2
Buffering action, maintains blood pH as it changes from oxyhemoglobin (carrying O2) to deoxyhemoglobin ( without O2)
Hemoglobin Reference Ranges
Adults Male 14-17.4 g/dL Female12-16.0 g/dL
Children Birth 13.5-20.0 g/mL 6-12 years 11.5-15.5 g/mL
**Refer to inside cover of text for other age ranges
Structure
4 polypeptide Subunits Heme group
Porphyrin ring Ferrous iron
Globin chain 2 Alpha Chains 2 Beta chains
Hemoglobin Synthesis
Synthesis Occurs in the mitochondria of developing red cells
as they mature in the bone marrow Processes necessary for normal synthesis
Adequate iron supply & delivery Adequate synthesis of protoporphyrins Adequate globin synthesis
Heme Synthesis
Chain of Events Iron delivery & supply
Iron is delivered to the reticulocyte by transferrin
Synthesis of protoporphyrins
Occurs in the mitochondria of RBC precursors
Mediated by EPO and vitamin B6
Protoporphyrin + iron = heme
Globin Synthesis
Chain of Events The rate of globin synthesis is
proportional to the rate of porphyrin synthesis.
Proper globin synthesis depends on genes. The precise order of amino acids in the globin chains is critical to the structure and function of hemoglobin.
Chain designations are as follows
Alpha α, beta β, delta δ, epsilon ε, gamma γ, zetaζ
Normal hemoglobins
Hemoglobin Synthesis
Oxygen transport
The amount of O2 bound to hemoglobin and released to tissues depends on PO2 and PCO2, but also the affinity of hemoglobin for O2.
Oxyhemoglobin: hemoglobin with oxygen Deoxyhemoglobin: hemoglobin without
oxygen Oxygen affinity is the ease with which
hemoglobin binds and releases oxygen.
Oxygen Affinity
Determines the proportion of O2 released to the tissues or loaded onto the cell at a given oxygen pressure.
Increases in oxygen affinity means hemoglobin has an increased affinity for O2, so it binds more. However, it does not want to give it up.
Decreases in oxygen affinity, cause O2 to be released.
Bohr Effect
Alterations in blood pH, shifts oxygen dissociation curve
In acidic pH, the curve shifts to the right Results in an enhanced capacity to release
O2 where it is needed
Oxygen Dissociation Curve
Right-Shift Hgb has less attraction
for O2
Hgb willing to release O2 to tissue
Examples: anemia, acidosis
Even though there may be less RBC’s, they act more efficiently to deliver O2
to target
Oxygen Dissociation Curve
Left shift Hgb has more
attraction for O2
Hgb less willing to release O2 to tissue
Examples: presence of abnormal Hgb’s, alkalosis
Carbon Dioxide Transport
Three mechanisms of transport Dissolution in the plasma Formation of bicarbonic acid Binding to carbaminohemoglobin
Nonfunctional hemoglobins
What do they do? Hypoxia
Inadequate amount of O2 in the blood
Cyanosis Presence of > 5 g/dl deoxyhemoglobin in blood Patient appears blue
Nonfunctional hemoglobins
Carboxyhemoglobin Oxygen molecules bound to heme are replaced by carbon monoxide. Slightly increased levels of carboxyhemoglobin are present in heavy
smokers and as a result of environmental pollution. Can revert to oxyhemoglobin.
Methemoglobin Iron in the hemoglobin molecule is in the ferric (Fe3) state instead of the
ferrous (Fe2) state. Incapable of combining with oxygen. Can occur as a result of strong oxidative drugs or to an enzyme
deficiency (more discussion to follow). Can revert to oxyhemoglobin
Sulfhemoglobin Hemoglobin molecule contains sulfur. Caused by certain sulfur-containing drugs or chronic constipation. Cannot revert to oxyhemoglobin and may cause death.
References
McKenzie, S. B. (2010). Clinical Laboratory Hematology (2nd ed.). Upper Saddle River, NJ: Pearson Education, Inc..